Articles as widely varied as decorative moldings, cultured marble and onyx tubs and vanities and boat hulls are today formed from settable compositions comprising suitable resins, chiefly at the present time poly(ester), urethane, olefin, and epoxy resins and suitable hardeners as necessary, filled with glass e.g. glass fiber, with clays, talcs, or similar mineral material useful to reinforce, fill, or add decorative effects to the resin. The term "poly(ester)" herein refers to polyesters such as polyethylene terephthalate product of terephthalic acid and ethylene glycol, and vinyl ester polymers as well.
These resins, together with their fillers, catalysts, colorants, and other typical components are formed on a molding surface, with or without pressure, enclosed or not, following pouring, spraying, layup, impregnation or other deposition onto the molding surface, which is typically precoated with a gel coat, typically isophthalic acid or orthophthalic acid-based polyester resin, to form a finish surface on the molded resin, subjected to air or heat setting, cure or hardening, and when set are removed from the mold. It may happen that the molded part sticks to the mold surface, particularly where the surface is other than a simple plane. In this event, either the part, or the mold, or both is liable to be harmed by efforts to separate the two, and fine stress lines may develop in molded parts subsequently processed. Sticking problems can be avoided by the use of an effective mold release agent interposed between the mold surface and the resin composition/gel coat applied to the mold. In practice it has been found that the effectiveness of these mold release agents is often not realized because coverage of the mold surfaces is incomplete, i.e. there are skipped areas, or holidays, or the coverage is inadequate, i.e. the depth of release agent coating is insufficient, even for a single molding operation. In practice, the molding operations are usually repetitive, producing a succession of replicate parts. Desirably the mold release agent will last through several cycles for manufacturing economy.
Whether the initial coating is complete and adequate, and what remains of it during successive cycles is presently difficult to determine. The release agents are typically fine waxes, usually synthetic organic polymers of low molecular weight such as those of high density and medium density polyethylene, blended to desired physical properties. The detection of such waxes in situ is difficult because they are transparent to water-white, tend to blend with the mold surface over time and even when visible there is insufficient contrast to make a judgment on adequacy of coverage even if coverage appears complete. The practical result of this situation is the too many or too few wax applications are used, with either course increasing manufacturing costs, and in the latter case risking expensive loss of parts or molds.
To increase the contrast of the mold release agent on the molding surface, as by using colored waxes, is counterindicated in nearly all situations, since the molded article must be free of wax color. Post-production removal of the wax color is both costly and ineffective, and may ruin the surface finish of the article, thereby making it unsalable.